1. Field of the Invention
This disclosure relates to video data buffers and, in particular, to a system and method for variable bit rate transmission using video data buffers.
2. Description of the Related Art
Video compression systems operating with constant bit rate encoding may implement the Motion Picture Experts Group (MPEG) standard of the International Standards Organization (ISO), as described in the MPEG standard specification; i.e. MPEG Test Model 4, "Coded Representation of Picture and Audio Information", ISO-IEC/JTC1/SC29/EG11, CCITT SG XV, Working Party XV/1, Document AVC-445b, February 1993. The MPEG standard specifies a Video Buffer Verifier (VBV) buffer as a model for a video decoder buffer. The system uses a Video.sub.-- Buffer.sub.-- Verifier Delay (VBV.sub.-- DLY) parameter inserted into the compressed video bitstream transmitted from the encoder to the decoder to synchronize the video encoder and decoder buffers. The parameter VBV.sub.-- DLY generated by the encoder is a measure of the time required to fill the decoder buffer from an empty state to an appropriate buffer level before the decoder is to remove the video data from the decoder buffer. The MPEG standard provides a method of calculating the VBV.sub.-- DLY parameter as a function of the encoder buffer level and the constant bit rate R of the transmission channel. The VBV.sub.-- DLY is calculated and inserted into the compressed video bitstream before it is sent to the encoder buffer for transmission to the decoder. Such compressed video bitstreams are produced by the encoder in such a manner as not to cause underflow or overflow in the decoder buffer.
For variable bit rate systems, the dependency of the system upon a transmission channel with a predetermined bit rate may be removed, while providing for proper video decoding without overflow or underflow. For such systems the MPEG standard does not specify a method to calculate the VBV.sub.-- DLY parameter. In such systems, buffer synchronization is performed in another manner.